1. Field of the Invention
This invention relates to an optical fiber component used in the field of optical communications, and more particularly to a temperature-compensated optical fiber component, suitably used in a WDM (Wavelength Division Multiplexing) communication system.
2. Description of the Related Art
Conventionally, a temperature-compensated optical fiber component is known which has an optical fiber grating as part of an optical fiber.
At the optical fiber grating, the effective refractive index of a core of the optical fiber is periodically changed along the axis of the optical fiber. The optical fiber grating is used for reflecting a light having a relatively narrow wavelength range which is called a Bragg reflection wavelength as a center wavelength. The Bragg reflection wavelength is determined by a Bragg grating period and the effective refractive index of the fiber core. Here, the Bragg reflection wavelength λ, the effective refractive index n, and the Bragg grating period Λ have the relationship expressed by the following equation (1):λ=2nΛ  (1)
For this reason, the optical fiber grating is usually referred to as the Bragg grating, and employed in the WDM communication system as a single-wavelength filter excellent in selecting a specific wavelength. However, the Bragg reflection wavelength λ has temperature dependency in respect of both of the effective refractive index n of the fiber core and the Bragg grating period Λ, as shown in the equation (1). Therefore, the temperature-compensated optical fiber component which employs a temperature-compensating package, as means for compensating or suppressing the temperature dependency of the optical fiber grating, is proposed.
Temperature-compensated optical fiber components have been proposed, for example, in Japanese Unexamined Patent Publication (Kokai) No. Hei 10-96827, and Japanese Unexamined Patent Publication (Kokai) No. 2000-347047. According to them, to enable temperature compensation of the above optical fiber components, a member having a negative coefficient of linear expansion is used. Alternatively, a combination of two kinds of members having different coefficients of linear expansion are used. More specifically, the optical fiber having a tension applied thereto beforehand is fixed or bonded to the above member(s), for example, by an organic adhesive, by which a negative temperature dependency is imparted to the Bragg grating period Λ of the Bragg grating. The negative temperature dependency of the Bragg grating period Λ is canceled by the positive temperature dependency of the effective refractive index n of the fiber core, which enabling the temperature compensation of the optical fiber component. As a result, the temperature dependency of the Bragg reflection wavelength λ is compensated for, whereby a stable monochromatic filter for use in the WDM communication system can be obtained.
However, the aforementioned temperature-compensating mechanism cannot effectively work if an external force is applied to the optical fiber component to deform a fiber-supporting portion, or the optical fiber component is used under circumstances where it is partially heated, or the predetermined tension applied to the optical fiber is changed with the lapse of time.